Stuttgart 2012 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 13: Poster 1: Cold Molecules, Femtosecond Spectroscopy, Molecular Dynamics

MO 13.29: Poster

Dienstag, 13. März 2012, 16:30–19:00, Poster.IV

Ultrafast Exciton Quenching upon Geometry Deformation in Molecular Aggregates — •Alexander Schubert¹, Volker Settels¹, Wen-Lan Liu^1,2, Frank Würthner¹, Christoph Meier³, Reinhold Fink^1,4, Stefan Schindlbeck⁵, Stefan Lochbrunner⁶, Bernd Engels¹, and Volker Engel¹ — ¹Universität Würzburg — ²Universität Heidelberg — ³Université de Toulouse — ⁴Universität Tübingen — ⁵LMU München — ⁶Universität Rostock

The efficiency of energy transport in molecular pi-aggregates is strongly attenuated by de-excitation mechanisms. We investigated experimentally and theoretically dimer aggregates of 3,4,9,10-perylene tetracarboxylic bisimide acid, exemplarily.

The measured absorption spectra could be interpreted assuming dipole-dipole coupling and a single effective vibrational monomer mode. An additional intermolecular torsional mode explained the fluorescence spectroscopic measurements indicating a long radiative lifetime and a low fluorescence yield. We now established an insight into the decay dynamics of optically excited state and the reaction path to the fluorescing state. Transient absorption measurements show that the excited state decays non-radiatively on an ultrafast fs-time-scale. This decay can be reproduced by a geometry change which increases the non-adiabatic transition effectivity. For that purpose we determined potential energy curves along a reaction coordinate relating the Franck-Condon geometry to a charge transfer configuration where the monomers exhibit the anion and cation geometry.